As the legislation dealing with environmental protection is tightened, the requirements set for the cleaning of exhaust gases are continuously becoming stricter. Also the use of various energy sources has become more and more critical, wherefore it is more recommendable to use the fuel released from a process, for instance CO gas, as fuel proper, rather than let it flow unused to the open air. The basic requirement for such usage of gas is that the gas is clean. In particular the cleaning of gases concerns industry, and it may even become a threshold issue with respect to the continuity of production. This also means that more and more enterprises will invest in gas scrubbing, both in research, development and production, as well as to related purchases.
An ideal solution in the case of a wet scrubber is a combined scrubber and droplet separator unit, whereto the exhaust gases can be separately conducted and removed in an ideal case directly to the open air, or, as regards fuel, directly to combustion.
Thus the scrubbing of gases can in a normal case be divided into two phases, to the scrubbing operation proper and to droplet separation thereafter. What is the ideal type of scrubber in each case depends a lot on the scrubbing principles and requirements. The same applies to the droplet separator.
A popular scrubber principle is the venturi principle. In practice these include two different types. The other uses a water jet to render power and energy to the scrubbing operation. In that case the jet simultaneously serves as a kind of blaster and extractor. According to another principle, the gas itself is the power-bringing element, wherefore the gas must be pressurized. In this specification we refer to the water-jet operated venturi by using the abbreviation WG scrubber element, and to the second, gas operated venturi by using the abbreviation GW scrubber element.
Detailed descriptions of both of the above mentioned scrubber types are found in the literature, for instance in the following references: (1) H. Bauer, Y. B. G. Varma: "Air pollution Control Equipment", Springer-Verlag, 1981 and (2) W. Strauss: "Industrial Gas Cleaning", Pergamon Press, 1966.
In venturi scrubbers, like in other scrubber types, one of the problems is caused by fluctuations in the capacity. In the patent publication FR 2,452,311, there is introduced an embodiment where an annular water layer forms in the venturi throat a collar for restricting the gas flow. It is easy to react to a change in the capacity by adjusting the thickness of the water layer.
The centrifugal force can also be utilized in scrubbers. A wet cyclone based on this principle is described, among others, in the U.S. Pat. No. 2,696,275 and on page 374 of reference (2), where a centrifugal wet scrubber, or a turbulence phenomenon created by means of baffle plates, is described.
The U.S. Pat. No. 3,456,928 describes a scrubber based on a blasting effect, where the gas flow is allowed to be blasted onto the surface of the water accumulated on the scrubber bottom.
Different types of droplet separators are described, among others, on pages 219-239 of reference (1). The main types of droplet separators are based on a zigzagging channel principle, on the centrifugal force principle or on the classic filter principle.
According to the U.S. Pat. No. 5,178,653, the gas or gases to be scrubbed are conducted to at least three vertical scrubber tubes, and after the scrubber tubes, the gases are conducted to a uniform droplet separator composed of several nested cylinders, in which droplet separator the gases are forced into turbulent motion, and a clean and dropless gas is discharged through an exhaust pipe located in the middle of the scrubber tubes.